It is known that during emplacement of a drill string it is necessary to maintain the upper part of the string with slips that usually include self-gripping jaws whose internal part has serrations or teeth that rest against the drill stem near the threaded female coupling and whose external part has a conical shape which meshes with a piece of corresponding shape to ensure self-gripping of the slips, thus holding the drill string that is suspended over its entire height.
In the technique now employed the teeth on the inner face of the slips that rest against the drill stem produce on the surface of the latter plastic deformations that are conveyed by a succession of notches. This causes a substantial reduction in resistance of the stem at the location where the self-gripping slips are applied, causing fatique rupture of the stem at this site, especially in the case where slanted holes are being drilled.
In other words, the notches, generally angular in shape, made by the slips on the drill stem substantially reduce its fatigue resistance which requires premature replacement of this stem or causes accidents.